Method of manufacturing fe and ni containing material, ferronickel mass using the fe and ni containing material and method for manufacturing the ferronickel mass

ABSTRACT

A method of manufacturing an Fe/Ni-containing material having a low content of sulfur from an Fe/Ni/SO 4 -containing liquid waste, a ferronickel mass using the Fe/Ni-containing material, and a method of manufacturing the ferronickel mass. The method includes: removing SO 4  from an Fe/Ni/SO 4 -containing liquid waste by adding an SO 4  neutralizing agent to the liquid waste so that pH of the liquid waste can be maintained to a pH level of 0.5 to 2.5; precipitating Fe and Ni in the form of hydroxide [(Ni,Fe)(OH)] by adding NaOH to the SO 4 -free solution; washing the precipitate with water; and manufacturing an Ni/Fe-containing material by filtering and drying the washed Ni/Fe-containing sludge. The method may be useful to suitably apply to the field of recycling of waste acids since an Fe/Ni-containing pellet and a high purity plaster are recovered as the stainless steel material from the waste water at the same time.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/600,107 filed Nov. 13, 2009, which is a national phase ofInternational Application No. PCT/KR2008/002701 filed May 15, 2008 andpublished in the English language, all of which are hereby incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a method of recycling Fe/Ni-containingwaste acids, and more particularly, to a method of manufacturing anFe/Ni-containing material from an Fe/Ni/SO₄-containing liquid waste, aferronickel mass using the Fe/Ni-containing material, and a method ofmanufacturing the ferronickel mass.

BACKGROUND ART

Waste acids containing Fe, Ni and SO₄ are generated when metalcomponents (nickel (Ni), iron (Fe)) are treated with sulfuric acid inthe method of manufacturing diamond.

In general, the liquid waste generated in the method of manufacturingdiamond includes 1 to 2% of Ni, 3 to 6% of Fe, and 30 to 40% of SO₄.

When Fe and Ni are present in the liquid phase, there is proposed amethod of separating Fe and Ni in the form of FeOOH and NiO andrecovering the Fe and Ni as an alternative to recycle Ni (Korean PatentApplication No. 1998-56697, Registered Patent No. 0406367)

The above-mentioned method of recycling an Fe/Ni sludge will bedescribed in detail, as follows.

That is to say, an iron chloride (FeCl₂)/nickel chloride(NiCl₂)-containing aqueous solution is prepared by dissolving anFe/Ni-containing sludge in hydrochloric acid so that the aqueoussolution can be adjusted to pH 3 to 4, and FeCl₂ is oxidized into FeCl₃by blowing air or hydrogen into the chlorides-containing aqueoussolution.

Next, the generated FeCI₃ reacts in water at pH 3 to 5 to form an orangeiron hydroxide (FeOOH) core, and an iron hydroxide sludge is formed byadding alkali to the iron hydroxide (FeOOH) core under the oxidationatmosphere so that the solution can be maintained up to twice mole of Fein the solution, and to pH 3 to 5.

Then, the formed iron hydroxide sludge is filtered to separate anNiCl2-containing filtrate from the iron hydroxide sludge, and the ironhydroxide sludge is then washed to obtain an iron hydroxide.

Finally, a nickel hydroxide precipitate is formed by adding alkali tothe separated filtrate so that the filtrate can be maintained to pH 10or more, and the nickel hydroxide precipitate is filtered, and washed toobtain nickel hydroxide.

However, the method of recovering and recycling iron hydroxide andnickel hydroxide as described above may apply only to chlorides.

That is to say, Fe and Ni are relatively easily separated from anFeCl₂/NiCl₂ aqueous solution, but when slaked lime as alkali is added toan SO₄-rich solution, a large amount of Ni is lost in the process ofremoval of Fe, which leads to the very low Ni recovery rate in themanufacture of nickel hydroxide.

In order to employ the Fe/Ni-containing material which is obtained fromthe liquid waste as a raw material of stainless steel, theFe/Ni-containing sludge is also subject to the drying and sinteringprocesses, but the Fe/Ni-containing sludge may be degraded in theseprocesses.

Therefore, in order to employ the Fe/Ni-containing material as thestainless steel material, it is necessary to agglomerate theFe/Ni-containing material into a pellet and the like.

In order to realize a desired strength of an agglomerated mass for rawmaterial of stainless steel according to the solidification method usingpowder of the Fe/Ni-containing material prepared according to theabove-mentioned method, the Fe/Ni-containing material is milled intopowder, and the powder may be agglomerated by adding an agglomerantadditive to the powder of the Fe/Ni-containing material, and mixing andmolding them.

However, the initial moisture content and the initial curing strength ofthe pellet are highly varied according to the resulting Fe/Ni-containingsludge.

In particular, when an FeNi sludge in an aqueous solution is formedthrough the wet reaction, the problem is that a short-term curingmoisture content of the FeNi sludge is high and a short-term curingstrength of the FeNi sludge is very low in the agglomeration(pelletizing) process.

Therefore, the curing time may be extended long when a mass, for examplea pellet, for a stainless steel material is manufactured using theNi-containing wet sludge as the stainless steel material.

DISCLOSURE Technical Problem

An aspect of the present invention provides a method of manufacturing anFe/Ni-containing material at a high recovery rate from anFe/Ni/SO₄-containing liquid waste, the Fe/Ni-containing material havinga low content of sulfur (S); a ferronickel mass using theFe/Ni-containing material; and a method of manufacturing the ferronickelmass.

Another aspect of the present invention also provides a ferronickel massmanufactured using the Fe/Ni-containing material, the ferronickel masshaving a high short-term curing strength, a low moisture content and ahigh Ni content; and a method of manufacturing the ferronickel mass.

Technical Solution

Hereinafter, exemplary embodiments of the present invention will bedescribed in detail.

According to an aspect of the present invention, there is provided amethod of manufacturing an Fe/Ni-containing material from anFe/Ni-containing liquid waste, including:

preparing an Fe/Ni/SO₄-containing liquid waste;

neutralizing and removing SO₄ from the liquid waste by adding an SO₄neutralizing agent to the liquid waste so that pH of the liquid waste ismaintained to pH 0.5 to 2.5;

precipitating Fe and Ni in the form of hydroxide [(Ni,Fe)(OH)₂] byadding NaOH to the SO₄-free solution;

washing the precipitate with water; and

manufacturing an Ni/Fe-containing material by filtering and drying thewashed Ni/Fe-containing sludge.

According to another aspect of the present invention, there is provideda method of manufacturing an Fe/Ni-containing material from anFe/Ni-containing liquid waste, including:

preparing an Fe/Ni/SO₄-containing liquid waste in which a value of[Fe(+3) ion concentration]/[Ni ion concentration+Fe(+2) ionconcentration] is 1 or less;

removing SO₄ from the liquid waste by adding an SO₄ neutralizing agentto the liquid waste so that pH of the liquid waste is maintained to pH0.5 to 4.5;

precipitating Fe and Ni in the form of hydroxide [(Ni,Fe)(OH)₂] byadding NaOH to the SO₄-free solution;

washing the precipitate with water; and

manufacturing an Ni/Fe-containing material by filtering and drying thewashed Ni/Fe-containing sludge.

According to still another aspect of the present invention, there isprovided a ferronickel mass including an Ni/Fe-containing sludgemanufactured by removing SO₄ by adding an SO₄ neutralizing agent to anFe/Ni/SO₄-containing liquid waste so that pH of the Fe/Ni/SO₄-containingliquid waste can be maintained to a pH level of 0.5 to 2.5,precipitating Fe and Ni in the form of hydroxide [(Ni,Fe)(OH)₂] byadding NaOH to the SO₄-free solution, washing the precipitate withwater, and drying the washed precipitate; and 10 to 20 parts by weightof a binder on the basis of 100 parts by weight of the dry sludge.

The ferronickel mass may further include a reducing agent.

When the binder is cement, the ferronickel mass may further include 10to 100 parts by weight of an austenitic stainless scale on the basis of100 parts by weight of the dry sludge.

The ferronickel mass may preferably include 4% by weight or more, andmore preferably 8% by weight or more of Ni.

According to still another aspect of the present invention, there isprovided a method of manufacturing a ferronickel mass using anFe/Ni-containing sludge manufactured through a wet reaction, including:

preparing a blended material by blending an Ni/Fe-containing sludgemanufactured by removing SO₄ by adding an SO₄ neutralizing agent to anFe/Ni/SO₄-containing liquid waste so that pH of the Fe/Ni/SO₄-containingliquid waste can be maintained to a pH level of 0.5 to 2.5,precipitating Fe and Ni in the form of hydroxide [(Ni,Fe)(OH)₂] byadding NaOH to the SO₄-free solution, washing the precipitate withwater, and drying the washed precipitate, and 10 to 20 parts by weightof a binder on the basis of 100 parts by weight of the dry sludge; and

agglomerating the blended material while adding moisture to the blendedmaterial.

The blended material may further include a reducing agent.

When the binder is cement, the blended material may further include 10to 100 parts by weight of an austenitic stainless scale on the basis of100 parts by weight of the dry sludge.

The ferronickel mass prepared in the above method may preferably include4% by weight or more, and more preferably 8% by weight or more of Ni.

According to still another aspect of the present invention, there isprovided a ferronickel mass including an Ni/Fe-containing sludgemanufactured by removing SO₄ by adding an SO₄ neutralizing agent to anFe/Ni/SO₄-containing liquid waste in which a value of [Fe(+3) ionconcentration]/[Ni ion concentration+Fe(+2) ion concentration] is 1 orless, so that pH of the Fe/Ni/SO₄-containing liquid waste can bemaintained to a pH level of 0.5 to 4.5, precipitating Fe and Ni in theform of hydroxide [(Ni,Fe)(OH)₂] by adding NaOH to the SO₄-freesolution, washing the precipitate with water, and drying the washedprecipitate; and 10 to 20 parts by weight of a binder on the basis of100 parts by weight of the dry sludge.

The ferronickel mass may further include a reducing agent.

When the binder is cement, the ferronickel mass may further include 10to 100 parts by weight of an austenitic stainless scale on the basis of100 parts by weight of the dry sludge.

The ferronickel mass may preferably include 4% by weight or more, andmore preferably 8% by weight or more of Ni.

According to yet another aspect of the present invention, there isprovided a method of manufacturing a ferronickel mass using anFe/Ni-containing sludge manufactured through a wet reaction, including:preparing a blended material by blending an Ni/Fe-containing sludgemanufactured by removing SO₄ by adding an SO₄ neutralizing agent to anFe/Ni/SO₄-containing liquid waste in which a value of [Fe(+3) ionconcentration]/[Ni ion concentration+Fe(+2) ion concentration] is 1 orless, so that pH of the Fe/Ni/SO₄-containing liquid waste can bemaintained to a pH level of 0.5 to 4.5, precipitating Fe and Ni in theform of hydroxide [(Ni,Fe)(OH)₂] by adding NaOH to the SO₄-freesolution, washing the precipitate with water, and drying the washedprecipitate, and 10 to 20 parts by weight of a binder on the basis of100 parts by weight of the dry sludge; and agglomerating the blendedmaterial while adding moisture to the blended material.

The ferronickel mass may further include a reducing agent.

When the binder is cement, the blended material may further include 10to 100 parts by weight of an austenitic stainless scale on the basis of100 parts by weight of the dry sludge.

The ferronickel mass may preferably include 4% by weight or more, andmore preferably 8% by weight or more of Ni.

Advantageous Effects

As described above, the method of manufacturing an Fe/Ni-containingmaterial may be useful to suitably apply to the field of recycling ofwaste acids since an Fe/Ni-containing pellet and a high purity plasterare recovered as the stainless steel material from the waste water atthe same time.

Also, the method of manufacturing an Fe/Ni-containing material may beuseful to provide a ferronickel mass with high productivity since it ispossible to effectively manufacture an Fe/Ni mass that satisfies adesired purity, such as Ni concentration, of a final product, as well asa desired physical properties such as short-term curing strength(short-term curing strength within 5 days) and moisture content(moisture content of a pellet cured within 5 days) in the process offorming a ferronickel mass using an Fe and Ni sludge.

BEST MODE

Hereinafter, exemplary embodiments of the present invention will bedescribed in more detail.

An Fe/Ni/SO₄-containing liquid waste is necessarily prepared tomanufacture an Fe/Ni-containing material from the Fe/Ni-containingliquid waste according to the present invention.

Next, SO₄ is neutralized and removed off by adding an SO₄ neutralizingagent to the liquid waste so that pH of the liquid waste can be adjustedto a pH level of 0.5 to 2.5.

According to the present invention, SO₄ is also removed off by adding anSO₄ neutralizing agent to the liquid waste so that pH of the liquidwaste can be adjusted to a pH level of 0.5 to 4.5 when a value of[Fe(+3) ion concentration]/[Ni ion concentration+Fe(+2) ionconcentration] is 1 or less in the liquid waste.

When the value of [Fe(+3) ion concentration]/[Ni ionconcentration+Fe(+2) ion concentration] exceeds 1 in the liquid waste,pH of the liquid waste may be adjusted to pH 1 or less by adding areducing agent to the liquid waste.

Slaked lime [Ca(OH)₂], NaOH and KOH may be used as the SO₄ neutralizingagent.

One example of using the slaked lime as the SO₄ neutralizing agent willbe described in detail, as follows.

In general, SO₄ in the waste acids is present in the form of H₂SO₄,FeSO₄, Fe₂(SO₄)₃, NiSO₄, etc.

When the slaked lime as the SO₄ neutralizing agent is added to anSO₄-containing solution, SO₄ is precipitated in the plaster form ofCaSO₄, and therefore it is possible to remove the SO₄ off by filteringthe SO₄-containing solution.

However, when the SO₄ is removed form the SO₄-containing solution byadding slaked lime as the SO₄ neutralizing agent, Fe and Ni areprecipitated in the form of hydroxides, and therefore it is nearlyimpossible to separate these components from the precipitated plaster.

Accordingly, the present inventors have made ardent attempts and foundthat an SO₄ component and Fe/Ni components may be effectively separatedfrom the waste acids by suitably adjusting a pH value in the solution,or a pH value and degree of oxidation, that is, a ratio of [Fe(+3) ionconcentration]/[Ni ion concentration+Fe(+2) ion concentration].Therefore, the present invention was completed on the basis of the abovefacts.

First, pH effects will be described in detail.

When slaked lime is added to a sulfuric acid (S), iron (Fe) and nickel(Ni)-containing solution (pH<O), SO₄ is precipitated.

When pH of the solution reaches pH 0.5 or more, the most of SO₄ in theform of sulfuric acid is precipitated in the form of plaster.

However, the metal (Fe and NI) ions and the plaster may beco-precipitated when pH of the solution is too high.

Therefore, pH of the liquid waste is preferably restricted to a pH levelof 0.5 to 2.5 according to the present invention.

That is to say, when the slaked lime is added to the liquid waste untilpH of the liquid waste is reduced below pH 2.5, only the plaster isprecipitated, but Fe(+2), Ni and Fe(+3) ions are present in the form ofion phase without being precipitated.

Meanwhile, when a value of [Fe(+3) ion concentration]/[Ni ionconcentration +Fe(+2) ion concentration] is 1 or less in the liquidwaste, pH of the liquid waste is preferably restricted to a pH level of0.5 to 4.5.

When an oxidizing agent such as hydrogen peroxide and nitric acid ispresent in the waste acids, a content of Fe(+3) is increased in thewaste acids due to the high degree of oxidation. In this case, theincrease in the content of Fe(+3) allows trivalent Fe ions to beprecipitated in the form of Fe sludge such as FeOOH and Fe(OH)₃ in thevicinity of pH=2.5-4.5.

Since the Fe sludge is very fine and has high moisture content, Ni ionis co-precipitated or occluded into the Fe sludge although the Ni ispresent in the form of iron sludge, and therefore the loss of Ni iscaused in the filtration of the Fe sludge.

Therefore, an iron hydroxide sludge having a strong ion occlusion shouldnot be formed to enhance a recovery rate of the Ni ion.

That is to say, in the present invention, when the value of [Fe(+3) ionconcentration]/[Ni ion concentration+Fe(+2) ion concentration] is 1 orless in the liquid waste, the precipitation of trivalent Fe ions in theform of Fe sludge such as FeOOH and Fe(OH)₃ should be suppressed with adecreasing content of Fe(+3).

In this case, the precipitation of Ni ion and Fe(+2) ion may besuppressed even when pH of the liquid waste is in a pH range of 2.5 to4.5.

Therefore, the use of an oxidizing agent such as hydrogen peroxide inthe waste acids should be inhibited as possible as it is.

As described above, when slaked lime is used as the SO₄ neutralizingagent, SO₄ is precipitated in the form of plaster. Therefore, it ispossible to remove the SO₄ and simultaneously obtain a plaster byfiltering the precipitate.

Preferably, the precipitated plaster should be filtered with a filteruntil the plaster is filtered to the dryness. However, since a smallamount of water is inevitably incorporated into the sludge, and Ni andFe ions are present in the aqueous solution, the sludge is filtered anddissolved in water, re-filtered to remove nearly all of the Fe and Niions (washing process).

When the washing solution is re-used in the subsequent neutralizationprocess, the recovery rate of the plaster may be extremely enhanced.

In particular, when the precipitated plaster is subject to the washingprocess, the Fe and Ni ions are removed completely, which leads to theimproved quality of the recovered plaster.

Then, Fe and Ni are precipitated in the form of hydroxide [(Ni,Fe)(OH)₂]when NaOH is added to the SO₄-free solution.

That is to say, when a sulfuric acid-soluble neutralizing agent, NaOH,is added to the SO₄-free Fe/Ni-containing solution, sulfuric acid isconverted into water-soluble sodium sulfate, and Fe and Ni ions areconverted in the form of hydroxides through the reaction represented bythe following Equation 1.

(Fe,Ni)SO₄+NaOH=(FeNi)(OH)₂+Na₂SO₄ (water-soluble)  Equation 1

Meanwhile, when NaOH or KOH is used as the SO₄ neutralizing agent, thesecomponents react with SO₄ ion to form Na₂SO₄ which is dissolved in theFe/Ni-containing solution, but the Fe and Ni ions are precipitated inthe form of hydroxides.

Then, the precipitate is washed with water.

Preferably, Ni—Fe ferrite is generated by blowing air or oxygen into theprecipitate and reacting them prior to washing the precipitate.

That is to say, when air or oxygen is blown into the precipitate andreacted with the precipitate, the Ni-Fe ferrite represented by thefollowing Equation 2 is generated as a black precipitate.

(FeNi)(OH)₂+O₂=(FeNi)O·Fe₂O₃(ferrite)  Equation 2

The Ni—Fe ferrite is preferably generated as described above. This iswhy the Ni—Fe ferrite has excellent filtering property, compared to theFe/Ni hydroxides.

However, it is desirable to subject nickel hydroxide to a ferriteprocess by blowing air or oxygen into the precipitate, but the oxidationreaction may be omitted since the long reaction time is required for thecomplete ferrite processing of the nickel hydroxide.

An Ni/Fe-containing material, that is, Ni/Fe hydroxide or Ni—Fe ferriteis prepared by filtering and drying the washed Ni/Fe-containing sludge.

According to the present invention, a recovery rate of theNi/Fe-containing material may reach 70% or more, and theNi/Fe-containing material also includes 2.0% or less by weight of S.

The Ni/Fe-containing material prepared according to the presentinvention may be especially suitably used as a stainless steel-meltingmaterial since the Ni/Fe-containing material includes 2.0% or less byweight of S.

In this case, it is apparent that the Ni/Fe-containing material may bepulverized into powder, depending on the use of the Ni/Fe-containingmaterial.

Also, the Ni/Fe-containing material [(FeNi)(OH)₂ or (FeNi)O.Fe₂O₃] asprepared in the above is used to manufacture a ferronickel mass forstainless steel-melting materials in the present invention, and themanufacturing of the ferronickel mass is described in detail, asfollows.

When the melting material is added to a furnace for the purpose of theuse as the stainless steel-melting material, the melting material isscattered in the form of powder, and therefore it is necessary toagglomerate the melting material.

The content of the Fe/Ni-containing hydroxide synthesized through theabove-mentioned wet neutralization reaction is varied according to theused materials, the Fe/Ni-containing hydroxide has an Ni content of 10%or more, and generally an Ni content of 10 to 20%, and the nickelhydroxide obtained by neutralizing an aqueous nickel solution has an Nicontent of approximately 35 to 45%.

According to the present invention, a blended material is prepared byblending 10 to 20 parts by weight of a binder with the Ni/Fe-containingsludge prepared in the above, based on 100 parts by weight of the drysludge. Then, the blended material is agglomerated into a ferronickelmass while adding moisture to the blended material.

The Ni/Fe-containing sludge includes an Ni/Fe-containing sludgemanufactured by removing SO₄ by adding an SO₄ neutralizing agent to anFe/Ni/SO₄-containing liquid waste so that pH of the Fe/Ni/SO₄-containingliquid waste can be maintained to a pH level of 0.5 to 2.5,precipitating Fe and Ni in the form of hydroxide [(Ni,Fe)(OH)₂] byadding NaOH to the SO₄-free solution, washing the precipitate withwater, and drying the washed precipitate, or an Ni/Fe-containing sludgemanufactured by removing SO₄ by adding an SO₄ neutralizing agent to anFe/Ni/SO₄-containing liquid waste in which a value of [Fe(+3) ionconcentration]/[Ni ion concentration +Fe(+2) ion concentration] is 1 orless, so that pH of the Fe/Ni/SO₄-containing liquid waste can bemaintained to a pH level of 0.5 to 4.5, precipitating Fe and Ni in theform of hydroxide [(Ni,Fe)(OH)₂] by adding NaOH to the SO₄-freesolution, washing the precipitate with water, and drying the washedprecipitate

As well as a cement binder, polyvinyl alcohol (PVA), molasses, starchand the like may be used as the agglomerating binder, and a blendingratio of the agglomerating binder is preferably in a range from 10 to 20parts by weight, based on 100 parts by weight of the dry sludge. This iswhy the strength of the Ni/Fe-containing material is low when theblending ratio of the binder is less than 10 parts by weight, and aconcentration of Ni is low when the blending ratio of the binder exceeds20 parts by weight.

Among the agglomerating binder, the cement binder is desirable in aneconomical aspect, and the cement binder includes at least one selectedfrom the group consisting of 3CaOSiO₂, 2CaOSiO₂, 3CaOAl₂O₃ and4CaOAl₂O₃.

When the cement binder is used as the agglomerating binder, the blendedmaterial preferably includes 10 to 100 parts by weight of an austeniticstainless scale on the basis of 100 parts by weight of the dry sludge inaddition to the cement binder.

The neutralized sludge generated through the wet reaction is completelysintered and dried to convert the hydroxide into its oxides, and thus tomanufacture a ferronickel mass. However, the ferronickel mass preparedthus has a low short-term curing strength and a high initial moisturecontent.

This is why the neutralized sludge generated through the wet reactionhas a high specific surface area since the neutralized sludge is fineand its OH group is reduced into water and exuded from the sludge in thesubsequent sintering process, which leads to the formation of poresinside the sludge.

From the copious experiments, the present inventors have found the factthat, when a test sample having a high specific surface area isagglomerated by adding an increasing amount of moisture, the test samplethat is subject to the agglomeration process has a high moisture contentand a low short-term curing strength due to the increasing amount ofmoisture.

Therefore, the use of additives having a high particle size andexcellent cementation reactivity are required to improve the strength ofthe Ni-containing sludge synthesized through the wet reaction.

The present inventors have also found that an Ni-containing scale isvery effectively used as the blending agent to improve the short-termstrength, the Ni-containing scale being formed in processing anaustenitic stainless steel product (so-called, 300-Series stainlesssteel).

The austenitic stainless scale is the most preferably an Ni-containingstainless scale that is generated in the shot blast process ofhot-rolled stainless steel products, or in the descaling process ofhot-rolled stainless steel products using high-pressure water.

Although the austenitic stainless scales are varied according to thescale-generating process, but one representative example of theaustenitic stainless scales is preferably an austenitic stainless scaleincluding 2 to 6% by weight of Ni, 6 to 15% by weight of Cr, 30 to 60%by weight of Fe, and the balance of oxygen and other impurities.

Since the austenitic stainless scale includes 2 to 6% by weight of Ni, ablending ratio of Ni may be increased without reducing an Ni content inthe ferronickel mass, which makes it possible for the ferronickel massto secure a high curing strength in the short term of time.

In this case, the short-term curing strength means a curing strengthwithin 5 days.

In particular, the stainless scale includes Fe and Cr components thatare helpful to the cement curing reaction. Therefore, the stainlessscale is very effectively used as the blending agent to improve theshort-term curing strength since the stainless scale may facilitate thecementation reaction when the stainless scale is mixed with a fine wetsludge and cured, and also form channels through which water addedduring the agglomeration process is discharged due to the large particlesize of the fine wet sludge.

A blending ratio of the stainless scale to the sludge generated throughthe wet reaction is preferably in a range of 10 to 100 parts by weight,based on 100 parts by weight of the dry sludge.

When the blending ratio of the stainless scale is less than 10 parts byweight, the short-term curing strength of the ferronickel mass is notimproved sufficiently. On the contrary, when the blending ratio of thestainless scale exceeds 100 parts by weight, the short-term curingstrength of the ferronickel mass is not improved any more by theaddition of the stainless scale, and the addition of the stainless scaleresults in the reduction of Ni content, which leads to the reduction ofthe Ni content in the final ferronickel mass.

Meanwhile, the blended material preferably further includes a reducingagent, and a content of the reducing agent is preferably present in acontent of 20 or less parts by weight, based on 100 parts by weight ofthe dry sludge.

The reducing agent functions to reduce FeNi oxides into metallic FeNi ina stainless steel melting furnace, and examples of the reducing agentinclude carbon, metallic aluminum, ferrosilicon, etc.

When the reducing agent is not blended in the ferronickel mass, it ispossible to manufacture the metallic FeNi by reducing the FeNi oxideswith a reducing gas such as hydrogen.

When the reducing agent is blended in an amount exceeding 20 parts byweight on the basis of 100 parts by weight of the dry sludge, theadditional increase in reduction rate is difficult and the cost of thereducing agent is increased by the addition of the reducing agent.Therefore, it is preferred to limit a blending ratio of the reducingagent to a range of 20 or less parts by weight on the basis of 100 partsby weight of the dry sludge.

When the reducing agent is blended in the ferronickel mass, thereduction reaction in which the reducing agent reduces FeNi oxides intometallic FeNi is represented, as follows.

(FeNi)O+C═FeNi+CO  Equation 3

(FeNi)O+Al═FeNi +Al₂O₃  Equation 4

(FeNi)O+FeSi=2FeNi+SiO₂  Equation 5

In order to manufacture the ferronickel mass according to the presentinvention, the blended material prepared thus is agglomerated by addingmoisture to the blended material.

The agglomeration method includes a pelletizing method, a briquettingmethod, an agglomeration method using an extruder, etc.

When the pelletizing method is used as the agglomeration method,moisture is added in an amount of 10 to 30% by weight based on the totalblended material. In the case of the briquetting method, moisture ispreferably used in an amount of 10 to 20% by weight based on the totalblended material.

The Ni content in the agglomerated ferronickel mass is preferablypresent in a content of 4% by weight or more, and more preferably 8% byweight or more.

That is to say, the Ni content in the ferronickel mass is preferablypresent in a content of 4% by weight or more in the aspect of supply,and preferably present in a content of 8% by weight or more inconsideration of the value of a product.

MODE FOR INVENTION

Hereinafter, exemplary embodiments of the present invention will bedescribed in more detail.

EXAMPLE 1

Hydrogen peroxide as an oxidizing agent and sodium thiosulfate as areducing agent were added to 1 kg of waste acids (containing 15 g of Ni)including 1.5% of Ni, 4.5% of Fe and 35% of SO₄ generated in the processof manufacturing diamond to prepare an aqueous solution whose degree ofoxidation is adjusted so that a value of [Fe(+3) ion concentration]/[Niion concentration+Fe(+2) ion concentration] can be in a range of 0.1 to3.

SO₄ was neutralized and precipitated to form a plaster sludge whilechanging pH of the solution until the pH of the solution becomes pH 0.3to 5.0 by adding an alkaline solution (including 5% of slaked lime)dropwise to the aqueous solution.

When the plaster sludge was formed in the aqueous solution, the plastersludge was filtered with a solid/liquid separator, and a 2 mole sodiumhydroxide solution was added to the plaster sludge-free filtrate toprecipitate Fe and Ni in the form of hydroxide at pH 10.0, which formsan Fe/Ni hydroxide sludge.

The air was blown into the Fe/Ni hydroxide sludge for 10 minutes toinduce the synthesis of Fe/Ni ferrite.

Then, 3 L of water (6 L of washing water in the case of Inventivematerial 6) was added to the sludge in which the Fe/Ni ferrite issynthesized, and dissolved metal ions such as sodium were washed, andthe resulting ferrite powder was filtered, dried and weighed. Contentsof Ni, Fe and S in the weighed test sample were measured using an energydispersive spectroscopy (EDX).

From the measurement results, an amount of recovered Ni was calculated,and a recovery rate of Ni was determined by comparing the amount ofrecovered Ni with an amount of Ni (15 g) in the waste acids includingNi, Fe and SO₄ as the reaction materials.

The reaction conditions of the ferrite powder containing the recoveredFe and Ni, and the components and recovery rate of the components aresummarized in the following Table 1.

TABLE 1 [Fe(+3) ion Metal Conc.]/ SO₄ ion [Ni ion SO₄ Ni Ni + Fe SNeutralizing neutralizing Conc. + Fe(+2) Removal Recovery ContentContent Example No. agent agent ion Conc.] pH rate (%) (%) ComparativeCa(OH)₂ NaOH 3 3.0 25% 40 0.5 material 1 Comparative Ca(OH)₂ NaOH 2 3.033% 41 0.8 material 2 Inventive Ca(OH)₂ NaOH 1 3.0 71% 42 0.8 material 1Inventive Ca(OH)₂ NaOH 0.25 3.0 88% 44 0.5 material 2 ComparativeCa(OH)₂ NaOH 0.25 5 53% 40 0.4 material 3 Inventive Ca(OH)₂ NaOH 0.1 2.095% 55 1.0 material 3 Inventive Ca(OH)₂ NaOH 2 1.0 94% 54 1.5 material 4Comparative Ca(OH)₂ NaOH 0.25 0.3 95% 33 2.2 material 4 InventiveCa(OH)₂ NaOH 0.25 2.0 95% 51 1.2 material 5 Inventive NaOH NaOH 0.25 2.093% 41 1.0 material 6 Comparative Ca(OH)₂ Ca(OH)₂ 0.25 2.0 99% 15 10.1material 5

As listed in the Table 1, it was revealed that, when only the slakedlime was used as the neutralizing agent as in Comparative material 5,SO₄, Fe and Ni metal ions were co-precipitated with a recovery rate of99%, but the recycling value of the sludge is very low since a largeamount of S component is incorporated into the sludge and Fe and Niconcentrations are relatively low.

Meanwhile, it was revealed that water-soluble sodium sulfate anhydrous(Na₂SO₄) was formed when NaOH was used as the neutralizing agent as inInventive material 6, and therefore the recovery rate of Ni is good andthe metal components are rich.

However, a large amount of the washing waster is required since NaOH isexpensive and the water-soluble sodium sulfate anhydrous (Na₂SO₄) isgenerated in a large amount.

Therefore, it might be seen that the SO₄ precipitation is morepreferably carried out using the slaked lime, and the metalprecipitation is also more preferably carried out using NaOH accordingto the present invention.

Meanwhile, when a value of [Fe(+3) ion concentration]/[Ni ionconcentration +Fe(+2) ion concentration] is greater than 1 as inComparative materials 1 and 2, a content of Fe(+3) is increased due tothe high degree of oxidation. In this case, when the content of Fe(+3)is increased in the waste acids, the most of trivalent Fe ions areprecipitated in the form of Fe sludge such as FeOOH and Fe(OH)₃ in thevicinity of pH=2.5-4.5. The Fe sludge

Since the Fe sludge is very fine and has high moisture content, Ni ionis co-precipitated or occluded into the Fe sludge although the Ni ispresent in the form of ion, and therefore the loss of Ni is caused inthe filtration of the Fe sludge.

Also, when the pH of the liquid waste is adjusted to pH 4.5 as inComparative material 3, the Ni component is directly precipitated, whichleads to the poor recovery rate of Ni.

Also, when the pH of the liquid waste is too low to precipitate sulfuricacid as in Comparative material 4, a sufficient amount of the sulfuricacid is not precipitated and removed off, expensive NaOH is increasinglyconsumed, an S content is rather increased in subsequent products, andother impurities such as magnesium are a little incorporated into Fe/Nioxides. Therefore, the liquid waste should be washed with a large amountof water.

On the contrary, when the value of [Fe(+3) ion concentration]/[Ni ionconcentration+Fe(+2) ion concentration] exceeds 1 as in Inventivematerials 1 to 6, the reducing agent such as sodium thiosulfate is addedto the liquid waste so that the value of [Fe(+3) ion concentration]/[Niion concentration+Fe(+2) ion concentration] can be maintained to 1 orless, or pH of the liquid waste can be maintained to a pH level of0.5-4.5 or a pH level of 2.5 or less, thus to prevent the precipitationof Fe ions.

Meanwhile, the Fe/Ni-containing sludges of the Inventive materials 1 to6 and the sludge of the Comparative material 5, all of which areprepared under the conditions as listed in Table 1 of the Example 1,were dried, the dried sludges were pulverized into powders. Coke as thereducing agent was added to each of the pulverized powders, and a cementbinding agent was used to prepare spherical pellets while addingmoisture to the pulverized powders in a pelletizer.

The prepared pellets were cured, and reduced in a stainless steelelectric furnace stimulator to obtain ferronickel metals. The Inventivematerials 1 to 6 showed good characteristics as the stainless steelmelting material.

However, the Comparative material 5 should be subject to the separatedesulfurization process since a ferronickel mass includes a large amountof S component due to the high content of the S component in theFe/Ni-containing sludge. As seen from the Table 1, it was revealed thatthe use as the stainless steel material is difficult since the recoveryrate of metal is low and slag is highly formed due to the lowconcentration of Fe+Ni.

EXAMPLE 2

Inventive materials 7 and 8 were prepared in the same conditions as inthe Inventive materials 2 and 4 of Example 1, respectively. That is tosay, slaked lime was added to the liquid waste to precipitate a plaster.Then, the precipitated plaster was separately filtered, and then washedwith an amount of water that is as much as 4 times the weight of theplaster in order to remove the remaining Ni and Fe ions. Then, thewashed plaster was re-filtered. In this case, the washing solution wasmixed with a filtrate obtained by filtering a plaster that is newlyprepared in the same manner as in the Inventive materials 2 and 4. NaOHwas added to the resulting mixture solution to precipitate Fe and Ni inthe form of hydroxide, that is, in the form of (Ni,Fe)(OH)₂. (Inventivematerial 2->Inventive material 7, Inventive material 4->Inventivematerial 8)

The resulting test sample was filtered, dried and weighed. Then,contents of the components in the weighed test sample were measuredusing an energy dispersive spectroscopy (EDX).

From the measurement results, an amount of recovered Ni was calculated,and a recovery rate of Ni was determined by comparing the amount ofrecovered Ni with an amount of Ni (15 g) in the waste acids includingNi, Fe and SO₄ as the reaction materials. The results are listed in thefollowing Table 2.

TABLE 2 Metal SO₄ ion [Fe(+3) ion Neutral- neutral- Conc.]/[Ni ion SO₄Ni Example izing izing Conc. + Fe(+2) Removal Recovery No. agent agention Conc.] pH rate Inventive Ca(OH)₂ NaOH 0.25 3.0 93% material 7Inventive Ca(OH)₂ NaOH 2 1.0 99% material 8

As listed in the Table 2, it was revealed that the recovery rate of Niis increased when compared to the Example 1, and Fe/Ni ions are alsoremoved from the separately recovered plaster to obtain a recyclableplaster having a white color.

Example 3

A Fe/Ni-containing sludge was prepared in the same conditions as in theInventive material 2 of the Example 1, and the Fe/Ni-containing sludgewas neutralized and dried to prepare a wet-process sludge.

Scales having 0% of Ni content (400-Series ferrite stainless scale),3.2% of Ni content (300-Series austenitic stainless steel; obtained inthe descaling process) and 4.5% of Ni content (300-Series austeniticstainless steel; obtained in the shot blast process), all of which wereprepared in the shot blast process and descaling process of stainlesssteel, were mixed with the prepared sludge so that contents of thescales can be in a range from 10 to 120 parts by weight based on 100 gof the prepared sludge.

Also, a cement binder and carbon as a reducing agent were mixed with thesludge so that contents of the cement binder and the reducing agent canbe in a range from 10 to 25 parts by weight and from 0 to 25 parts byweight, respectively, based on 100 g of the prepared sludge.

The blended material as prepared thus was homogenized in a mixer, andthen palletized in a rotation plate of a pelletizer whiled adding waterto the blended material.

The ferronickel pellet prepared thus was cured at intervals of 1, 3 and5 days, and measured for strength and moisture content according to thecuring periods. Also, The cured ferronickel pellet was completely cured,and the Ni content in the ferronickel pellet was then analyzed. Theresults are listed in the following Table 3.

TABLE 3 Amount of Kind/Amount Amount 1 day - 3 day- 5 day- TestWet-process added stain- of added of added Strength/ Strength/ Strength/Ni sample sludge (Ni less scale/ reducing cement Moisture MoistureMoisture content in No. content) Ni content agent binder content contentcontent final pellet 1 FeNi(OH)₂ — C/10 15  8 kg/cm²/33% 15 kg/cm²/28% 24 kg/cm²/22% >8% (13%Ni) 2 FeNi(OH)₂ 25 g/3.2% C/10 15 19 kg/cm²/22%35 kg/cm²/15%  45 kg/cm²/10% >8% (13%Ni) 3 FeNi(OH)₂ 45 g/4.5% C/10 1525 kg/cm²/20% 41 kg/cm²/12% 65 kg/cm²/8% >8% (13%Ni) 4 FeNi(OH)₂ 45g/0%  C/10 15 24 kg/cm²/21% 39 kg/cm²/11% 64 kg/cm²/8% 7.5%  (13%Ni) 5FeNi(OH)₂ 80 g/4.5% C/10 15 28 kg/cm²/20% 45 kg/cm²/11% 78 kg/cm²/7% >8%(13%Ni) 6 FeNi(OH)₂  5 g/3.2% C/10 15 10 kg/cm²/31% 17 kg/cm²/25%  29kg/cm²/21% >6.9%  (13%Ni) 7 FeNi(OH)₂ 120 g/3.2%  C/10 15 29 kg/cm²/19%45 kg/cm²11% 78 kg/cm²/7% >6.9%  (13%Ni) 8 FeNi(OH)₂ 45 g/4.5% —/0  1527 kg/cm²/20% 43 kg/cm²/11% 66 kg/cm²/8% >8% (13%Ni) 9 FeNi(OH)₂ 80g/4.5% C/10 5  9 kg/cm²/36% 18 kg/cm²/27%  19 kg/cm²/22% >8% (13%Ni) 10FeNi(OH)₂ 100 g/3.2%  C/10 25 28 kg/cm²/20% 44 kg/cm²/11% 69 kg/cm²/8%7.0%  (13%Ni)

As seen from the Table 3, it was revealed that, when the stainless scaleis not mixed with the sludge (Test sample 1), the ferronickel pellet hasa short-term curing strength (within 1 to 5 days) lower than the minimumstandard strength (40 kg/ cm2) that is required to add the ferronickelpellet into an electric furnace. In general, it is necessary to cure theferronickel pellet for 15 to 30 days so as to satisfy requirement of theminimum standard strength.

Meanwhile, it was revealed that, when a suitable amount of the stainlessscale is mixed with the sludge (Test samples 2 to 5, 7, 8 and 10), theferronickel pellet has an excellent short-term curing strength.

However, it was revealed that, when the Ni-free stainless steel, thatis, a ferrite (400-Series) scale is mixed with the sludge (Test sample4), the curing strength of the ferronickel pellet is a little improvedby the addition of the Ni-free stainless steel, but the Ni content inthe ferronickel pellet is low.

Also, it was revealed that, when the blending ratio of the stainlessscale is less than 10 parts by weight based on 100 parts by weight ofthe dry sludge (Test sample 6), the short-term curing strength of theferronickel pellet is not improved properly, whereas, when the blendingratio of the stainless scale exceeds 100 parts by weight (Test sample7), the short-term curing strength of the ferronickel pellet is notimproved any more by the addition of the stainless scale, and theaddition of the stainless scale results in the reduction in the Nicontent, and therefore the final ferronickel pellet has a low Nicontent.

Furthermore, it was revealed that, when the blending ratio of the binderis less than 10 parts by weight (Test sample 9), it is difficult toimprove the curing strength of the ferronickel pellet, whereas the Nicontent in the ferronickel pellet is low when the blending ratio of thebinder exceeds 20 parts by weight (Test sample 10).

1-44. (canceled)
 45. A ferronickel mass, comprising: an Ni/Fe-containingsludge manufactured by removing SO₄ by adding an SO₄ neutralizing agentto an Fe/Ni/SO₄-containing liquid waste in which a value of [Fe(+3) ionconcentration]/[Ni ion concentration+Fe(+2) ion concentration] is 1 orless, so that pH of the Fe/Ni/SO₄-containing liquid waste is maintainedto a pH level of 0.5 to 4.5, precipitating Fe and Ni in the form ofhydroxide [(Ni,Fe)(OH)₂] by adding NaOH to the SO₄-free solution,washing the precipitate with water, and drying the washed precipitate;and 10 to 20 parts by weight of a binder and 20 parts by weight or lessof a reducing agent on the basis of 100 parts by weight of the drysludge.
 46. The ferronickel mass of claim 45, wherein the binder is atleast one selected from the group consisting of cement, polyvinylalcohol (PVA), molasses and starch.
 47. The ferronickel mass of claim46, further comprising 10 to 100 parts by weight of an austeniticstainless scale on the basis of 100 parts by weight of the dry sludgewhen the binder is cement.
 48. The ferronickel mass of claim 45, whereinthe reducing agent is at least one selected from the group consisting ofcarbon, metallic aluminum and ferrosilicon.
 49. The ferronickel mass ofclaim 47, wherein the austenitic stainless scale comprises 2 to 6% byweight of Ni, 6 to 15% by weight of Cr, 30 to 60% by weight of Fe, andthe balance of oxygen and other impurities.